The reactions of a wide variety of trisubstituted phosphorus compounds with substances which may lead to pentasubstituted phosphorus compounds will be investigated. If pentasubstituted compounds are formed, then the mechanism of their formation will be investigated. In the main this will be done to decide if their formation involves direct insertion of the phosphorus into the bond or whether a stepwise reaction path is followed. Evidence is accumulating to the effect that both kinds of reactions are possible. The first is a novel biphilic displacement process where as the second is a more conventional nucleophilic displacement process. A study will be made of exchange reactions of simple phosphoranes, such as pentaethoxyphosphorane, with various alcohols and polyhydroxy compounds. Previous work has shown that new phosphoranes are often formed by these exchange reactions, and it is hoped that new interesting materials can be prepared by these reactions. Various cycloaddition reactions will be investigated as routes to penta-coordinate phosphorus compounds. Previous work has shown that such compounds often form by these condensations. There has been no general study of 1,3-cycloaddition reactions, which is the area to be investigated. There will also be a continued effort to make full use of our extensive nmr capability both in solving problems generated in this research and also in cooperative efforts with other groups who are being supported by NIH.